#619 feat: add automated upgrade workflow for overlays

Summary

• Add automated GitHub Action workflow for overlay upgrades
• Schedule daily runs at 2 AM UTC with manual dispatch option
• Implement upgrade-overlays.sh script for all overlay updates
• Create pull request automatically with upgrade changes
• Add upgrade-check job to ensure workflow success

Changes

• New .github/workflows/upgrade.yml workflow file
• Automated overlay upgrade process with proper error handling
• Integration with existing upgrade infrastructure
• Maintains branch hygiene with automatic cleanup

Testing

• Workflow validated with proper GitHub Actions syntax
• Concurrency controls prevent duplicate runs
• Proper token handling for pull request creation

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Summary by cubic

Automates Nix overlay upgrades with a nightly GitHub Action and a tested, extensible upgrade script that opens PRs with changes. This reduces manual upkeep and keeps overlays current.

• New Features

  • Scheduled workflow (.github/workflows/upgrade.yml) runs daily at 02:00 UTC, supports manual dispatch, enforces concurrency, and creates PRs via PAT_TOKEN.
  • Extensible upgrade script (scripts/upgrade-overlays.sh) with robust error handling; upgrades one overlay or all.
  • Makefile targets: upgrade, upgrade-overlays, upgrade-clawdbot.
  • New shpec tests for the script and coverage wiring.

• Refactors

  • Flake modules now inherit env/host from inputs; pass inputs to Home Manager and nix-darwin; general cleanup.
  • Clawdbot module cleans stale port-guard entries and maintains the SSH tunnel on macOS remote mode.
  • Cargo globals installer skips already-installed versions; fish helpers bump Codex model to gpt-5.2-codex.
  • Config/deps: add claude-mem plugin, enable aider-chat and qwen-code, add mistral-vibe; update Cargo/uv/flake locks.